Contact lens molds are used to form contact lenses in contact lens production systems. The contact lens molds consist of two mold halves which define a contact lens forming cavity therebetween. During production, a solidifiable contact lens material in liquid form is deposited into a first mold half and the other mold half is positioned over the first mold half. Mold engaging apparatus then closes the mold to shape and cure the liquid contact lens material to form a contact lens. To ensure that a suitable contact lens is manufactured, it is important that the two mold halves are mated precisely. If the mold halves are not mated precisely, lens abnormalities may result which could cause discomfort to the wearer and/or not accurately correct the wearer's vision.
FIG. 1 depicts a prior art contact lens molding apparatus for forming a contact lens. The molding apparatus comprises a front curve mold half 104, a back curve mold half 108, a carrier 102, and an engaging member 116. A liquid contact lens material 106 between the front curve mold half 104 and the back curve mold half 108 forms a contact lens between the mold halves during molding. The back curve mold half 108 is used to shape the surface of the contact lens which will be positioned on a wearer's eye and the front curve mold half 104 is used to shape the other surface of the contact lens. The contact lens formed between the mold halves 104, 108 contains a centrally located optical zone for vision correction surrounded by a peripheral zone used to correctly position and mount the contact lens on an eye. The front curve mold half 104 is supported by the carrier 102 and the back curve mold half 108 has flanges 109 for receiving the engaging member 116.
The engaging member 116 depicted in FIG. 1 contains an engaging surface 116A (represented by the bottom edge of the engaging member 116). The mold is closed, thereby shaping the contact lens material 106, by moving the engaging member 116 toward the carrier 102 to engage the flanges 109 on the perimeter of the back curve mold half 108 and drive it toward the front curve mold half 104. Typically, the shaped contact lens mold material is then cured (i.e., hardened) by subjecting the material to light.
Presently, contact lenses are produced using contact lens production line systems. The production line systems provide supporting carriers which move through a series of stations with different steps required to form contact lenses performed at each station. FIG. 2A and FIG. 2B depict a mold engaging station in a non-engaged state and an engaged state, respectively, and a carrier 102 which moves from station to station during the formation of the contact lenses. The carrier 102 contains a plurality of indentations 102A for receiving the molds and materials for forming contact lenses. An example of a contact lens production line system can be found in U.S. Pat. No. 6,071,440 to Wang et al., entitled Contact Lens Production Line Pallet System, incorporated fully herein by reference.
At a first station during the formation of contact lenses, the front curve mold halves 104 are placed into the plurality of indentations 102A of the carrier 102. The carrier 102 then moves from station to station where a liquid contact lens material 106 is deposited into the front curve mold halves 104, the back curve mold halves 108 are positioned over the front curve mold halves 104 containing the liquid contact lens material 106, and the front curve mold halves 104 and the back curve mold halves 108 are engaged and the contact lens material 106 is cured.
At the mold engaging station depicted in FIG. 2A and FIG. 2B, the engaging surfaces 116A engage the flanges 109 of the back curve mold halves 108 and drive the back curve mold halves 108 towards the front curve mold halves 104. Ideally, the portion of the back curve mold halves 108 which corresponds to the optical zones of the resultant lenses will not flex, excess liquid contact lens material 106 is able to be expelled, and the centers of the front curve mold halves 104 and of the back curve mold halves will be aligned so that a contact lens formed therebetween will have a desired shape (e.g., desired thicknesses) with little decentration (side-to-side difference between the center of the front surface of the contact lens and the center of the back surface of the contact lens). If the decentration and thicknesses are unacceptable, the lenses are discarded, thereby reducing production yields and driving up costs.
Decentration and improper thicknesses may result from improper alignment between the front curve mold halves 104 and the back curve mold halves 108 and flexing of the back curve mold halves 108 during the formation of the contact lenses. In contact lenses with decentration, the edges of the contact lenses may be uneven, causing discomfort to the wearer. In addition, improper thicknesses may affect the ability of the contact lenses to adequately correct a wearer's vision.
In addition, excess liquid contact lens material 106 between the mold halves 104,108 may need to be expelled to prevent lenses having improper thicknesses. Typically, when the back curve mold halves 108 are driven toward the front curve mold halves 104 a seal is created near the perimeter of the mold halves 104,108, thereby preventing excess liquid contact lens material 106 from being expelled. Once the flow of liquid contact lens material 106 is stopped, applying more force to the flanges 109 makes a tighter seal. The excess liquid contact lens material 106 trapped by the seal prevents the back curve mold halves 108 from seating all of the way in the cavities of the front curve mold halves 104, thereby further contributing to improper lens thicknesses.
Prior art systems attempt to resolve the problem of decentration by providing registration apertures 114 in the carrier 102 and corresponding registration pins 112 associated with the engaging members 116 in order to precisely align the engaging members 116 over the appropriate indentations 102A of the carrier 102. In these systems, however, when the back curve mold halves 108 are placed off center of the indentations 102A at a previous station, decentric lenses will still be formed as the engaging surfaces 116A attempt to drive the back curve mold halves 108 straight down.
In addition, even if the engaging members 116 and back curve mold halves 108 are aligned precisely over the appropriate indentations 102A, driving the back curve mold halves 108 toward the front curve mold halves 104 by supplying a force to the flanges 109 on the perimeters of the back curve mold halves 108 may result in flexing of the back curve mold halves 108 and trapping excess liquid contact lens material 106, thereby affecting the shape of the resultant contact lenses.
In order to produce contact lenses that have uniform edges and proper thicknesses, precise closure of the contact lens molds is important. Improper closure may result in decentric lenses which produce discomfort to the wearer and misshaped lenses that reduce the subjective comfort of the wearer. Since the proper closure of the mold assemblies is crucial, methods and apparatus for closing the mold assemblies properly to produce well shaped contact lenses with minimal decentration constitute a long felt need in the field of the invention.